Effective technology for removing, recovering, and cleaning up oil spills or oil slicks from the surface of sea water and shorelines are still needed. Typically, the collection of such spills are carried out by applying materials that absorb and/or adsorb the oil. Adsorption is the adhesion of molecules to the surface of the material and typically results in the oil coating the surfaces (pores and capillaries) of the adsorbent material. Adsorbent materials typically have a microcrystalline matrix that is not readily penetrated by the oil and therefore does not swell when adsorbing oil. On the other hand, absorption is the penetration of molecules to the bulk phase of the material and typically results in the oil contained within the absorbent material. Affinity between the oil and absorbent material drives oil molecules into the absorbent matrix. Highly, absorbent materials are usually oil soluble. Cross-linking of such materials is required to maintain the integrity of the absorbent and prevent its dissolution into the oil.
There have been some studies reporting the sorption (sorption is the general term for adsorption and/or absorption) of spilled oils with inorganic mineral products (i.e. clay, silica, zeolites, etc.) and organic vegetable products (straw, corn cob, peat moss, wood fiber, cotton fiber, etc.) (M. O. Adebajo, R. L. Frost, R. L., J. T. Kloprogge, O. Carmody, S. Kokot, “Porous materials for oil spill cleanup: a review of synthesis and absorbing properties”, J. Porous Materials, 2003, 10, 159-170). Most of these materials show limited oil absorption capacity and also absorb water; therefore the oil absorbers that are recovered are unsuitable for calcination. Many of these products end-up in land fields after use.
Several synthetic fibers, including crystalline polyethylene and polypropylene (PP) fibers (U.S. Pat. No. 5,639,541) and meltblown polypropylene pads and booms (Bayat, et al., Chem. Eng. Technol. 2005, 28, 1525) have been disclosed; these materials generally recover oil in their interstices by capillary action. Because the weak oil-substrate interaction, the fiber-based sorbers exhibit many disadvantages, including failure to maintain oil of low viscosity, easy re-bleeding of the sorbed oil under a slight external force, and poor recovery of oil after it has sunk in water.
There are patents disclosing the use of synthetic resins, such as cross-linked styrenic and acrylic copolymers, which absorb oil in their hydrophobic molecular structure. Cross-linking is needed to prevent the polymer from dissolving in the oils (U.S. Pat. Nos. 5,239,007; 5,641,847; and 5,688,843). Such material have the advantage of selectively absorbing oil floating on the surface of water, and have good oil-maintaining properties of absorbed oil. However, these synthetic resins have the drawback of a long absorbing time in comparison with that of fibers. In particular, they fail to absorb high viscosity oil within a short time. Some methods, i.e. milling the oil absorber to increase surface area, were proposed to improve the oil absorbing speed for high viscosity oil, but were met with limited success. The milled oil absorbers are liable to aggregate, thereby the gel block phenomenon prevents the admission of oil to be absorbed into further gaps between the particles of oil absorber.
Further, there are literature reports disclosing the use of cross-linked styrene/acrylate (Jang, et al., J. Appl. Polym. Sci. 2000, 77, 903), 1-octene/acylate (Atta, et al., J. Appl. Polym. Sci. 2005, 97, 80), and octadecene/maleic anhydride copolymers (Atta, et al., J. Appl. Polym. Sci. 2007, 105, 2113). However, these resins contain some hydrophilic polar groups and require additional procedures for cross-linking reaction after copolymerization, and having the drawback of a long absorbing time, especially for aliphatic hydrocarbon components. Some synthesized rubbers, such as polybutadiene (Shan, et al., J. Appl. Polym. Sci. 2003, 89, 3309), butyl rubber (Ceylan, et al., Environ Sci. Technol. 2009, 43, 3846), SBR (Fouchet, B., J. Appl. Polym. Sci. 2009, 111, 2886), and EPDM (Zhou, et al., J. Appl. Polym. Sci. 2003, 89, 1818), were also modified (grafting and cross-linking) to achieve the network structure for oil absorption. However, the solution cross-linking procedure typically used with such materials is not controlled. Moreover, these materials usually require extensive solvent extraction to remove any soluble polymer fraction prior to use (Zhou, et al., J. Appl. Polym. Sci. 2002, 85, 2119), and the resulting sol-free materials possess various degree of cross-linking density that reduces the overall oil swelling capability. Some methods, i.e. milling, electric-spinning, and foaming of the oil absorbents to increase surface area, were applied to improve the oil absorbing speed. However, these materials, similar to that of meltblown PP, just physically adsorb oil at the surface by capillary action, and thereby intrinsically prevent the further penetration of oil into matrixes.
Accordingly, there is a continuing need for absorbent materials that can quickly collect and retain hydrocarbons and other such contaminates, as is necessary in the case of oil spills and oil contaminated areas and liquids. Furthermore, there is also a need for absorbent materials that can advantageously minimize the treatment of the absorbent after use, including waste disposal, and improve recyclability and biodegradability of the recovered absorbent and its contents.